1. Field of the Invention
The present invention relates to an ignition device for an internal combustion engine provided with a noise-suppressing resistor for suppressing noise generated at the time of a discharge of an spark plug disposed in a high-voltage tower.
2. Description of Related Art
Conventionally, in an ignition device for an internal combustion engine disclosed, for example, in JP 2004-232466 A (FIG. 1, paragraph 0011), a noise-suppressing resistor 8 disposed in a high-pressure cylinder 7 is connected at one end thereof to a high-voltage terminal 6 and at the other end thereof to a coil spring 23 which is electrically connected to an apex terminal 33 of an spark plug 32. A cast insulating resin 5, which is injected into a case 4 so as to insulate and fix a transformer, is cured, whereby the noise-suppressing resistor 8 is held electrically connected to the high-voltage terminal 6 in the high-pressure cylinder 7.
The noise-suppressing resistor 8 is, generally, constructed by connecting and fixing electrodes to both ends of a ceramic resistor respectively, and is used for the purpose of preventing electrical noise generated at the time of a spark discharge of the spark plug 32 from affecting peripheral electronic components.
In the aforementioned ignition device for the internal combustion engine, however, the noise-suppressing resistor 8 and the high-voltage terminal 6 are fixed by the cast insulating resin 5 so as to prevent abrasion from being caused between the noise-suppressing resistor 8 and the high-voltage terminal 6 due to, for example, engine vibration. Thus, there have been problems in that a crack is produced in the cast insulating resin 5 as a result of a difference in coefficient of linear expansion arising between the cast insulating resin 5 made of an epoxy resin and the noise-suppressing resistor 8 made of a ceramic, and the noise-suppressing resistor 8 is damaged by a thermal stress ascribable to the cast insulating resin 5.
There has also been a problem in that the noise-suppressing resistor 8 and the high-voltage terminal 6 must be connected to each other in advance of injecting the cast insulating resin 5 into the case 4 with a view to preventing the noise-suppressing resistor 8 and the high-voltage terminal 6 from being brought out of electrical contact with each other due to the interposition of the cast insulating resin 5.